1. Technical Field
The present invention is related to a communication apparatus, a communication method, a circuit module and an integrated circuit, which perform multi-carrier communication operations among a plurality of communication apparatuses, while these communication apparatuses are connected to a transmission channel and share a communication band.
2. Background Art
Since transmission systems such as the OFDM (Orthogonal Frequency Division Multiplexing) system using a plurality of sub-carriers have such a great merit that high quality communications can be carried out even in a severe transmission channel, these transmission systems are utilized not only in wireless communications, but also in wired communications such as power line communications. Generally speaking, frequency bands from 2 MHz to 30 MHz are used as the frequency bands of the power line communications (refer to, for example, Patent Publication 1). In addition, technical ideas capable of utilizing broadband covering higher frequency bands than the above-described frequency band are recently considered.
Also, other technical ideas capable of equalizing levels of time waveforms in order not produce peaks and capable of suppressing interference and the like are proposed in multi-carrier communications with employment of a plurality of sub-carriers. In the above-described peak suppressing technical ideas, in such a case that a large peak is not present in time waveforms, phases of respective sub-carriers are rotated by using a default phase vector, whereas in such a case that a large peak may be monitored, a phase vector is changed so as to search such a phase vector by which the peak is not produced. Then, the phases of the respective sub-carriers are rotated by the searched phase vector (refer to, for example, Non-patent Publication 1). In multi-carrier communications, such peak suppressing technical ideas constitute essential techniques to decrease a difficulty in design of power amplifiers.
In the case that a plurality of different logic networks are formed by employing communication apparatuses such as power line communication apparatuses connected to transmission channels, security among these different networks is maintained by employing network keys and the like. In general, technical specifications of these communication apparatuses connected to the respective networks are identical to each other. In other words, phase vectors which are employed in order to suppress peaks are also identical to each other. With employment of the above-described technical ideas, even among the networks which are different from each other in physical layer levels of communication apparatuses, signals of the respective networks can be sensed (carrier sensing is available); if the CSMA (Carrier Sense Multiple Access) technique and the like are utilized, then it is possible to suppress collisions of signals; and even when the different networks are present relatively close to each other, communications can be smoothly carried out.
The technical idea described in the Patent Publication 1 has the following purpose: That is, even in such a case that the plural sorts of communication apparatuses whose communication systems are different from each other are connected to the shared transmission channel, the collisions of the signals are avoided without executing the demodulating process operation and the like which may cause relatively heavy loads, and signals outputted from other communication apparatuses can be readily sensed. In accordance with this technical idea, such a condition for indicating whether or not a communication request signal of a control period is present may change a slot allocation of a data period subsequent to the control period. Then, since a communication request signal is rotated by a phase vector, the communication request signal can be firmly sensed. However, a detailed description is not made of a slot allocation of a data domain. Thus, in this technical idea, there are some possibilities that data capable of satisfying a required delay time cannot be firmly transmitted.    [Patent Publication 1] JP-A-2007-135180    [Non-patent Publication 1] Denis J. G. Mestdagh and Paul M. P. Spruyt, “A Method to Reduce the Probability of Clipping in DMT-Based Transceivers”, IEEE Transactions on Communications, Volume 44, No. 10, pages 1234 to 1238, in 1996